Scientists have long wondered why woolly mammoths became extinct. We've delved into such possibilities as inbreeding, climate change, human hunting, and an asteroid impact. None of these solutions have proven particularly satisfying — mostly because, as a new study suggests, no single cause can be attributed to their extinction. The mammoths, it would seem, died out slowly as the world changed around them.

We usually think of woolly mammoths as purely Ice Age creatures. But while most did indeed die out…
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Woolly mammoths once ruled over the Northern Hemisphere in a region paleontologists call the mammoth steppe. Their remains are particularly common in Beringia, the bridge of land that connects eastern Russia and western Alaska. But their long reign ended only a few thousand years ago, leaving today's scientists searching for a reason why.

To tackle this problem, paleoecologist Glen MacDonald at the University of California, Los Angeles, and his team tracked the pattern of the Beringian mammoth's extinction. They combined a geographical database of mammoth finds with radiocarbon dates for mammoth remains, prehistoric plants, and archaeological sites to follow how woolly mammoth populations ebbed and flowed during the past 45,000 years.

What they discovered is that woolly mammoth numbers declined as the cold climate of the Pleistocene gave way to a warmer, wetter one. Their populations were largely dictated by changes to the environment and where they happened to be geographically located. By the end of the Last Glacial Maximum, about 20,000 years ago, Northern populations of mammoths declined while populations in Siberia's interior increased. And during the Younger Dryas period, about 11,500 years ago, mammoths started to concentrate in the North, including some that become isolated on islands. It was at this time that warmer climates were converting the mammoth steppe into conifer forests, peat bogs, and shrublands — unhappy places for mammoths.

The island mammoths were the last of their breed, holding out against a gradual extinction that was taking place on the mainland.

What's important to note from the study is that no single cause can be attributed to their demise. The researchers explain that climate change drastically altered their habitats, causing their numbers to shrink. Prehistoric humans moving through Beringia likely played a contributing factor, adding insult to what was already a serious injury.

MacDonald and his team contend that the extinction took place over a protracted period of time, and in turn, have come to reject the "Blitzkrieg'-style" explanations for end-Pleistocene extinctions.